The present disclosure is directed to the use of MAX phase solids mixed with polymers to form an outer air seal of a turbine engine, for enhanced thermal conductivity and improved abradability to protect the blade tips from overheating.
Fan blade technology uses abradable coatings for fuel burn reduction and increases in temperature capability. In some fans, a coating is applied to the airfoil portion of the fan. Abradable systems can be susceptible to efficiency losses and premature failure due to high rub forces, rough coating surfaces, local heat generation, high coating temperature, coating spallation, and durability issues in certain environments. There are several requirements to mitigate issues associated with abradable coatings, such as improved abradable damage tolerance and toughness, improved thermal cycling and durability, and reduced frictional forces and low coefficient of friction, self-lubrication and low energy of cut, high abradable thermal conductivity and higher erosion resistance and desired wear ratio.
The abradable seal is typically positioned between a stationary component on the opposite side of a rotating component. For example, the stationary component may be an outer engine casing or a shroud and the rotating component may be a blade tip, a sealing ring, a knife-edge seal, and the like. In operation, the blade initially engages the abradable seal and rubs or cuts into the abradable seal. The abradable seal helps ensure that the blade tip does not contact the outer casing, it is the abradable material of the seal that is removed, rather than the blade tip. The abradable seal prevents damage to components of gas turbine engines during rubs thus allows operation at reduced clearances between the stationary component and the rotating component. Minimizing clearance between the abradable seal and the rotating component also reduces leakage over the blade tip, resulting in increased efficiency and power output.
Current aluminum fan blades are polyurethane coated to enhance erosion resistance. The aluminum blade tips rub against polymer based abradable outer air seal coatings. The heat generated by friction during a rub event conducts into the airfoil introducing a temperature rise which in turn may result in the polyurethane coating blistering. High surface temperatures and heating of the blades occur due to low thermal conductivity of the polymer based abradable outer air seal coating. There is a need for improved capability and increased thermal conductivity of abradable outer air seal coatings in order to mitigate temperature rise in such airfoils during rub events and prevent spallation and blistering of polyurethane coatings from the blades.